1. Field of the Invention (Technical Field)
This invention generally relates to firearms, and specifically to an improved fire control trigger mechanism for machine guns and methods of making and using such mechanism.
2. Background Art
The only trigger assemblies in current production and use for M-16 rifles are the M-16A1 lever-selected mechanism ("Safe-Semi-Auto") and the M-16A2 three-round burst mechanism. A four position selector/trigger assembly exists which combines "safe," "semi," "burst" and "auto" modes, but is only in very limited production.
The M-16A2 burst mechanism comprises a ratchet-and-pawl mechanism which limits the full automatic mode of fire to a three-round maximum thereby requiring trigger release and pull to initiate another three-round burst. The three-round burst mechanism has been criticized by some because it does not reset if less than three rounds are fired. This renders the subsequent burst either one, two or three rounds. Further, trigger pull varies at each point of the burst cycle; unpopularity of the burst mode of fire has resulted in deliberate disablement of the ratchet-and-pawl mechanism by troops in the field.
The Steyr-Aug machine gun does control selection of rate of fire with the trigger, but its design could not be incorporated into the M-16 without totally redesigning the M-16 rifle.
U.S. Pat. No. 2,716,923, to Gaidos, entitled "Firing Mechanism for a Rifle," issued Sep. 6, 1955, perhaps most pertinently, provides semi or full automatic fire modes based upon trigger pull alone. However, Gaidos requires an extremely complex trigger and sear mechanism not adaptable to modern M-16 use. Similarly, U.S. Pat. No. 3,290,993, to Irusta, entitled "Release Mechanism for Automatic Firearms," issued Dec. 13, 1966, discloses selective finger-engaging trigger portions enabling either semi-automatic or full automatic fire. U.S. Pat. No. 2,533,283, to Pierce, entitled "Trigger Mechanism," issued Dec. 12, 1950, discloses full automatic to semi-automatic fire in the obsolete Browning Automatic Rifle (M1918) by a selective fire lever. U.S. Pat. No. 2,512,638, also to Gaidos, entitled "Fire Control Selector for Automatic Firearms," issued Jun. 27, 1950, also discloses a selector lever for selecting either semi-automatic or full automatic fire.
U.S. Pat. No. 5,115,588, to Bronsart, et al., entitled "Trigger Mechanism for Firearms," issued May 26, 1992, discloses a trigger mechanism for bolt action pistols enabling an adjustable sear engagement. U.S. Pat. No. 2,367,280, to Hyde, entitled "Control Means," issued Jan. 16, 1945, discloses a trigger-actuated mechanism for controlling the operation of a semi-automatic rifle to single shot operation. U.S. Pat. No. 3,446,114, to Ketterer, entitled "Trigger Mechanism for Automatic Firearms," issued May 27, 1969, discloses a mechanism for converting semi-automatic fire to full automatic fire, or from closed bolt firing operation to open bolt firing operation.
U.S. Pat. No. 4,937,964, to Crandall, entitled "Two-Stage Triggered Adapter," issued Jul. 3, 1990, and U.S. Pat. No. 5,187,312, to Osborne, entitled "Two Stage Trigger Assembly," issued Feb. 16, 1993, both relate to trigger assemblies providing triggers with two distinct trigger "pulls," thereby indicating imminence of weapon discharge. No functional change in operation of the weapons is imparted by these mechanisms.
It seems clear that the prior art lacks teachings of a simple trigger mechanism specifically designed to alter rate of fire in M-16s and other weapons having a full automatic rate of fire by trigger pressure alone.